Sunday, 1 February 2015

Magnetos Part 1

A magneto is what provides the igntion on most old bikes pre-1960s. Its a rotating coil inside a stationary magnet, when the contact breaker opens it sends a HT pulse to the sparking plug and, with fuel and air, it goes bang. Mine doesn't, at least it does when cold, and will run when hot, but it won't start when hot - a classic sign of imminent magneto failure.

My magneto is a BTH KC1:-

The usual cause of magneto demise is the condenser which is buried in the armature. One remedy is to fully strip and rewind the armature along with a new condenser, or you can snip the old condenser out and fit an external one. This is my plan. Fit one of these:-

Still got to strip part of the armature but hopefully this should fix the bad starting.